Trailing edge flaps are known to influence the aerodynamic characteristics of wind turbine blades. WO 2004/088130 (Forskningscenter Risø, Bak et al.) discloses a wind turbine blade comprising one or more shape deformable trailing edge airfoil sections comprising actuator means for providing shape changes in the shape deformable trailing airfoil sections. WO 2004/088130 discloses the use of ‘smart materials’ and mechanical actuators integrated in a deformable materiel changing the outer geometry in the leading and trailing edge region and thereby changing the blade section aerodynamic forces. Such ‘smart materials’ are said to deform once a voltage is applied to them. Preferred materials are said to include: shape memory alloys, piezoelectric materials, magnetostrictive materials, electrorheological fluids, electrochromic materials, electroactive polymers, chiral materials, conducting polymers, photoactive materials, thick and thin films, optical fibres, tunable dielectrics, self monitoring materials, self assembly materials, self repairing/healing materials, biomaterials, power supplies, power sources, and self powering, multilayer and composite materials and/or ‘smart composites’.